Holographic character reader

ABSTRACT

Apparatus for recognizing serially viewed characters of a known font of type is achieved by imaging the characters onto a substrate bearing an electrically charged liquid photoconductor medium deformable in accordance with the optical image. When the deformed portion of the medium is rotated into the beam of a pulsed laser, spots are imaged upon a matrix of photodetectors by passing the laser beam emergent from the medium through a multiple spatial filter made by positioning the type for each of the expected characters in a vertical line.

KR 3956613137 SR ana m United States Patent Charles Q. Lemmond Scotia,N.Y.

Nov. 28, 1967 Feb. 23, 1971 General Electric Company a corporation ofNew York [72] Inventor [21 Appl. No. [22] Filed [45] Patented [73]Assignee [54] HOLOGRAPHIC CHARACTER READER 9 Claims, 6 Drawing Figs.[52] US. Cl 250/219, 340/141.3, 350/35, 346/74 511 int. Cl 606k 9/00250/219 [50] Field of Search (CR), 237; 356/71, 74; 350/160, 161, 162(SF), 3.5(H0bg), 3.5(SF); 340/1463; 346/74; 96/11 [56] References CitedUNITED STATES PATENTS 3,195,396 7/1965 Horwitz et a1. 356/71 POWER SUPPLY OIRECT/ON 0F TERI/EL 3,274,565 9/1966 Wright 250/219X 3,291,60112/1966 Gaynor 346/74X 3,435,244 3/1969 Burckhardt et a1. 250/219XPrimary Examiner-Walter Stolwein AttorneysRichard R. Brainard, MavinSnyder, Paul A.

Frank, Frank L. Neuhauser, Melvin M. Goldenberg and Oscar B. WaddellABSTRACT: Apparatus for recognizing serially viewed characters of aknown font of type is achieved by imaging the characters onto asubstrate bearing an electrically charged liquid photoconductor mediumdeformable in accordance with the optical image. When the deformedportion of the medium is rotated into the beam of a pulsed laser, spotsare imaged upon a matrix of photodetectors by passing the laser beamemergent from the medium through a multiple spatial filter made bypositioning the type for each of the expected characters in a verticalline.

PATENTEU FEB 2 3197| SHEET 1 BF 2 In ve n tor:

Char/es QLemmond Hl's Atto may,

HOLOGRAPE'IIIC CHARACTER READER BACKGROUND OF THE INVENTION Thisinvention relates to holography, and more particularly to a holographiccharacter reader using a liquid photoconductor for recording inputimages.

The problem of automatic character identification in opera tions whereindifferent sets of graphic characters are displayed at high frequencyrates has, in the past, presented formidable technological obstacles.One area in which this problem is of particular importance, for example,is in sorting mail. If it were possible to automatically identify onlythe address ZIP codes so as to facilitate sorting by mechanical meansaccording to postal zones, the need in Post Offices for manual sortingof mail with U.S. addresses could be restricted solely to sorting by boxnumber or street address. This would result in a great decrease in costof mail handling, along with elimination of human error involved inmisreading the ZIP codes. Other examples of where rapid characteridentification would be advantageous include railroad caridentification, operations in which articles on a moving conveyor beltare labeled with printed characters, and in fact any type of system inwhich items may be identified by alphanumeric characters incorporatedthereon.

The advent of holography has resulted in a powerful new tool for patternrecognition. For example, in the Autonomous Space Navigation System ofJ. M. Holeman and JD. Welch, application Ser. No. 622,965, filed Mar.14, 1967 and assigned to the instant assignee, holography is employed toobtain optically a fix or positional information in space. Moreover,holography is also employed to identify graphic characters, as in theGraphic Character Recognition System of J. E. Bigelow and C. Q. Lemmond,application Ser. No. 560,419, filed Jun. 27, 1966 now U.S. Pat. No.3,374,717 and assigned to the instant assignee. However, in theaforementioned Bigelow and Lemmond application, the graphic characterscomprising input data to be identified are detected initially by avidicon camera tube. The present invention permits omission oftelevision apparatus in reading graphic characters at a high rate ofspeed, thereby effectuating a significant reduction in complexity ofapparatus and attendant costs.

BRIEF SUMMARY OF THE INVENTION Accordingly, one object of the inventionis to provide a simplified character recognition system capable ofidentifying in essentially real-time, images of alphanumeric characterspresented in rapid succession.

Another object is to provide a graphic character recognition systemwherein each image of characters to be identified is inserted in thepath of coherent light rays without first undergoing transformation fromvisible to electromagnetic signal form.

Another object is to provide a character recognition system wherein themedium for recording the visible image displayed to the system iscontinually usable without heat development and with essentially nothermal gradients introduced therein.

Briefly, in accordance with a preferred embodiment of the invention, animprovement in a graphic character recognition system of the type whichincludes a source of coherent radiation pulses, radiation detectingmeans responsive to the radiation, spatial filter means interposedbetween the source of coherent radiation and the radiation detectingmeans, and media bearing sets of characters to be recognized, isprovided. This improvement comprises a substrate coated with adeformable liquid photoconductor and situated intermediate the sourceand the filter means. Means are provided for illuminating sequentiallyeach of the media in order to image the set of characters on each mediumonto a region of the liquid photoconductor coating and deform the regionaccordingly. Means are also provided for situating the deformed regionof the coating in the path of the coherent radiation.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention believedto be novel are set forth with particularity in the appended claims. Theinvention itself, however, both as to organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of the character recognition system of theinstant invention;

FIG. 2 is an illustration of the image on the input plane in the systemof FIG. 1;

FIG. 3 illustrates a typical order in which the characters to berecognized are arranged prior to being recorded in the multiple spatialfilter in the system of FIG. 1.

FIG. 4 illustrates images of optical recognition spots as produced atthe input to the detecting means in the system of FIG. 1;

FIG. 5 illustrates a second embodiment of the character recognitionsystem of the instant invention; and

FIG. 6 illustrates a third embodiment of the character recognitionsystem of the instant invention.

v DESCRIPTION OF THE PREFERRED EMBODIMENTS The character reader of theinstant invention is schematically illustrated in FIG. I. A thin,transparent disc I0 comprised on a conducting material 9, such asstannic oxide, overlaid on a transparent dielectric base 8, such asglass, and coated with a liquid material bearing a suitablephotoconductor 11 on one surface thereof, is situated in the pulsed beamof coherent light emitted by a laser 12 operated from a power supply 3i.The laser light beam is passed from disc I0 through a multiple spatialfilter 13 to impinge upon light detecting means, such as aphotodetecting diode matrix 14. Matrix I4 is offset form the optic axis19 so as to respond to first order images, or diffraction imagesimmediately adjacent the optic axis. Multiple spatial filters and amethod of making are described in detail in J. M. Holeman and C. Q.Lemmond application Ser. No. 492,187 filed Oct. 1, 1965 and assigned tothe instant assignee.

A second, momentary beam of light is produced by a source of light whichmay be incoherent, such as a flashlamp is operated from a power supply32, and illuminates a medium 16, shown as an envelope bearing, togetherwith its address, alphanumeric characters to be identified, such as theZIP code 17. These characters are of a known font of type and located ina predetermined position as, for example, the lower righthand comer ofthe envelope. Operation of laser 12 and flashlamp 15 is coordinated withthe detected appearance of each of media 16 bearing characters II! to beidentified, through a synchronizer 30 which is actuated by detectingmeans such as a lamp 33 providing a beam of light to a photodetector orphotocell 34. Thus, if media 16 are transported on a conveyor (notshown) in the direction of travel indicated, power supplies 31 and 32are actuated in synchronism with the appearance of each one of media 16on the conveyor. To properly position each envelope to be sensed by thesystem, a vertical member'35, which is moved by a shaft 36 in thedirection indicated by the double arrow, slides each envelope on theconveyor against a stationary member 37. Both member 35, which ismoveable with respect to envelope I6, and member 37, which is stationarywith respect to the envelope, are carried along on the conveyor.

The light produced by flashlamp l5, which is selected to be of awavelength falling within the sensitivity range of liquid photoconductorll on disc 10, impinges upon the photoconductor in a region which may besubstantially diametrically opposite the region on which the beam ofcoherent light from laser 12 impinges, since light from flashlamp l5reflected from medium 16 is directed by a reflector 13 onto disc ii). Ahigh voltage corona discharge is produced by electrodes 20 which areconnected to a DC source of high voltage 21. The corona dischargeproduces a continuous electric field which is directed across thethickness of the liquid photoconductor so as to establish an electricalcharge on the surface of the photoconductor. This charge is applied tothe photoconductor in a region which is adjacent and immediately aheadof the location at which light from flashlamp impinges on thephotoconductor. Disc 10, which is shown partially cut away to illustratethe position of electrodes 20, is driven by a synchronous motor 22 inthe direction indicated by the arrow, so that the newly charged regionof the photoconductor is immediately thereafter positioned in the pathtaken by light reflected from medium 16. Conductive layer 9 on disc 10is grounded through the shaft and housing of motor 22.

The laser beam is widened and collimated by a pair of lenses 23 and 24respectively, while light emerging from transparent disc 10 is imaged bya lens 25 onto multiple spatial filter 13. Similarly, light emergingfrom spatial filter 13 is imaged by a lens 26 onto photodiode matrix 14.Characters 17 to be identified are likewise imaged by a lens 27 ontoliquid photoconductor coating 11 on disc 10.

A suitable liquid photoconductor film 11 may be cast from a suspensionof 1.2 grams of copper phthalocyanine such as Ciba Microlith Blue 4 GTtoner (available from Ciba Pharmaceutical Products, Inc., Summit, NewJersey) in 19 grams of a highly viscous liquid polymer ofpoly-a-methylstyrene such as Dow Resin 276 V9, (available from DowChemical Company, Midland, Michigan) dissolved in about grams oftoluene. A one-half hour bake at 85 C. suffices to remove enough of thesolvent from the film for suitable operation. For a photoconductor filmof this type, the corona electrodes typically comprise sharp tips onshort lengths of wire, for example about 1 inch of 10 mil diameternickel wire, with the tips mounted about i to 2 inches above the filmsurface, and from 2.5 kilovolts to -10 kilovolts of DC voltage on thetips Alternatively, other types of liquid photoconductors may be used,such as those described in J. Gaynor application Ser. No. 526,757, filedFeb. 11, 1966, now U.S. Pat. No. 3,450,837, and assigned to the instantassignee.

In operation, disc 10 is continuously rotated at a constant speed bymotor 22. Medium 16, bearing the alphanumeric characters to beidentified, is precisely positioned beneath flashlamp 15, as by aconveyor (not shown) and members 35 and 37 carried along on theconveyor, and is illuminated momentarily by the flashlamp for a fractionof a millisecond. The image of the alphanumeric characters is focused bylens 27 and reflector 18 onto liquid photoconductor film 11 on disc 10in the region of the film bearing a charge newly supplied by electrodes20. As the disc is rotated in the indicated direction, the chargedregion on which the alphanumeric characters are imaged undergoes achange in resistivity according to a pattern corresponding to the imageof the characters, as described in J. Gaynor Pat. No. 3,291,601, issuedDec. 13, 1966 and assigned to the instant assignee, so that theelectrical charge on the surface of the film in those portions of thefilm illuminated by the light of the flashlamp will become electricallyneutral. Since the coating is in liquid form, the remaining chargescause the liquid to deform so as to produce a three dimensionalrecording of the alphanumeric characters to be recognized. Because thecoating is in liquid form at room temperatures, no heat development isrequired.

As the disc continues to rotate, the electrical charge image onphotoconductor film 1 1 is next positioned in the path to be taken bythe coherent light produced by laser 12. Laser 12 is preferably a pulsedlaser, synchronized through synchronizer 30 and photodetector 34 withthe rate at which media 16 appear, and coordinated with the angularvelocity of disc 10, which is driven by a synchronous motor operated,for example, from a commercial 60-cycle AC source. Thus, laser 12 emitsa momentary pulse of light each time the portion of liquidphotoconductor film 11 deformed in accordance with the image produced bya flash of light from flashlamp 15 has been positioned by disc 10 in thepath of coherent light emitted by the laser. The laser light produces aFourier transform of the imaged alphanumeric characters as it emergesfrom disc 10, and this transform is imaged by lens 25 onto multiplespatial filter 13 which contains a plurality of diffraction patternscorresponding to those produced by all of the characters expected to berecognized by the system. In this instance, the multiple spatial filteris fabricated as described in the aforementioned Bigelow et al.application Ser. No. 560,419 and Holeman et al. application Ser. No.492,187, with the characters to be recognized, here the ten decimaldigits, positioned in a vertical line in the manner illustrated in FIG.3. Since the input transparency borne by disc 10 contains a horizontalformat of alphanumeric characters to be recognized, as shown in FIG. 2,it is possible to identify each character in the image and determine itsordinal position in the image according to its vertical and horizontallocation respectively in the recognition plane. Thus, FIG. 4 illustrateshow the recognition spots of light 40, each of which comprises the firstorder image emergent from spatial filter 13, are related in position tothe arrangement of characters from which the filter was made and thearrangement of the input characters to be recognized, for an assumedinput image made up of the characters 12304. Each spot of light 40,shown in FIG. 4, represents its individual location on photodiode matrix14, while each quadrilateral 41 within matrix 14 represents anindividual photodetector of the matrix.

Coherent light from laser 12 in the configuration of FIG. 1 passesthrough disc 10 and photoconductive film ll thereon to spatial filter 13and thence to photodiode matrix 14. Since the positions in the matrix ofthe photodetectors which sense the light spots are determined by thenumbers in the ZIP code and the order in which they appear in the ZIPcode, it is clear that the ZIP code number is coded by the position ofthe photodetectors which respond to spots of light. Also since thephotodetectors are subjected to one of two light levels dependent uponthe presence or absence of light spots, it is clear that the output isof one or two levels and therefore may be considered digital. Output ofphotodiode matrix 14 comprises a digitally coded signal which maycontrol operation of utilization means, such as a letter sorter for usein a Post Office if automatic identification of ZIP codes is beingperformed. Photodiode matrix 14 could, in the alternative, be replacedwith a scanning image tube, such as a vidicon or an image orthicon,thereby removing constraints on the ZIP code location except forrotational position constraint; in this instance however, a logiccircuit, such as that described in the aforementioned Bigelow et al.application Ser. No. 560,419, would be required to determine the orderin which the recognition spots were scanned by the scanning beam.Regardless of whether radiation detecting means 14 comprises aphotodiode matrix or a scanning image tube however, the short timeinterval which elapses between the instant an input image is detected bythe system and the instant at which the characters have been recognizedas determined by the electrical output signals produced by radiationdetecting means 14 provides the system with essentially real-timerecognition capability.

FIG. 5 illustrates another embodiment of the holographic characterreader. In this embodiment, electrodes 20 are rotated at a constantangular velocity by a motor 51 in a direction opposite to the rotationof disc 10. High voltage source 21 is connected to electrodes 20 througha brush 52 in contact with a slip ring 53 mounted on the shaft of motor51. By rotationally passing electrodes 20 over the surface of liquidphotoconductor 11, the photoconductor can be evenly charged so thatlight imaged thereon can deform the photoconductor. Reapplication of aneven charge on the photoconductor prior to focusing another light imagethereon, achieved by another pass of electrodes 20 over the surface ofthe photoconductor, restores the surface of the photoconductor to a flatconfiguration, enabling application of a new image thereon.

FIG. 6 illustrates yet another embodiment of the holo graphic characterreader of the invention. In this embodiment, both electrodes 20 and disc10 are made to rotate in opposite directions, as in the apparatusillustrated in FIG. 5. However,

by use of a beam splitter 58 instead of a mirror to image the charactersto be recognized onto liquid photoconductor 11, with the beam splittersituated in the path of coherent light emitted by laser 12 so as to passcoherent to the liquid photoconductor, the characters to be recognizedare imaged onto the disc within the path of the coherent light. in thisembodiment, it is not necessary that disc be rotated at all; however,some slight rotation of the disc may be desirable in order to keep theliquid photoconductor evenly dispersed over the entire surface ofgrounded conductive layer 9, provided the rotational speed is low enoughto allow a brief interval between occurrence of the flashlamp pulse andthe laser pulse during which the liquid photoconductor can deform. Byuse of a xenon flashlamp in all embodiments of the invention,deformation of the liquid photoconductor occurs due to its sensitivityto the wavelength of light (blue-green) produced thereby. By use of ahelium-neon laser, for example, to produce the coherent read-out beam,the wavelength of the readout beam is only at the red end of the opticalspectrum, and thus produces no deformation of the liquid photoconduc-01.

The foregoing describes a simplified graphic character recognitionsystem capable of identifying, in essentially realtime, images ofalphanumeric characters presented in rapid succession Each image ofcharacters to be identified is inserted in the path of coherent lightrays without first having undergone transformation from visible toelectromagnetic si nal form. The medium for recording the visible imagedisplayed to the system is continually usable without heat developmentand with essentially no thermal gradients introduced therein.

While only certain preferred features of the invention have been shownby way of illustration, many modifications and changes will occur tothose skilled in the art. it is, therefore, to be understood that theappended claims are intended to cover all such modifications and changesas fall within the true spirit and scope of the invention.

I claim:

l. in a graphic character recognition system having essentiallyreal-time recognition capability and including a source of coherentradiation pulses, radiation detecting means positioned in the path ofsaid radiation, spatial filter means interposed between said source ofcoherent radiation and said radiation detecting means, and media bearingsets of characters to be recognized, the improvement comprising: asubstrate coated with a deformable liquid photoconductor and situatedintermediate said source and said filter means; means for momentarilyilluminating each of said media in sequence; optical means for imagingthe set of characters on each medium when illuminated onto a region ofthe liquid photoconductor coating so as to deform said regionaccordingly; and means for situating the deformed region of said coatingin the path of said radiation.

2. The character recognition system of claim 1 wherein said means forilluminating sequentially each of said media comprises a flashlamp andmeans for moving said media in relation to said flashlamp.

3. The character recognition system of claim 1 including meanssynchronizing said source of coherent radiation pulses with said meansfor illuminating sequentially each of said media.

4. The character recognition system of claim 2 including meanssynchronizing said source of coherent radiation pulses and said meansfor illuminating sequentially each of said media with the rate at whicheach one of said media is detected.

5. The character recognition system of claim 1 wherein said means forsituating the deformed region of said coating in the path of saidradiation comprises means mechanically coupled to said substrate forimpelling said substrate to transport the deformed region of saidcoating into the path of said radiation.

6. The character recognition system of claim 5 wherein said substratecomprises a disc and said means for impelling said substrate comprises asynchronous motor.

7. The character recognition system of claim 5 including means forestablishing an electrical charge on the surface of said coating in theregion of said coating immediately ahead of the location at which saidcharacters are imaged onto said coating.

8. The character recognition system of claim 5 wherein said source ofcoherent radiation pulses comprises a laser and said radiation detectingmeans comprises an array of photodetectors.

9. The character recognition system of claim 6 including means forestablishing an electrical charge on the surface of said coatingimmediately ahead of the location at which said characters are imagedonto said coating.

1. In a graphic character recognition system having essentiallyreal-time recognition capability and including a source of coherentradiation pulses, radiation detecting means positioned in the path ofsaid radiation, spatial filter means interposed between said source ofcoherent radiation and said radiation detecting means, and media bearingsets of characters to be recognized, the improvement comprising: asubstrate coated with a deformable liquid photoconductor and situatedintermediate said source and said filter means; means for momentarilyilluminating each of said media in sequence; optical means for imagingthe set of characters on each medium when illuminated onto a region ofthe liquid photoconductor coating so as to deform said regionaccordingly; and means for situating the deformed region of said coatingin the path of said radiation.
 2. The character recognition system ofclaim 1 wherein said means for illuminating sequentially each of saidmedia comprises a flashlamp and means for moving said media in relationto said flashlamp.
 3. The character recognition system of claim 1including means synchronizing said source of coherent radiation pulseswith said means for illuminating sequentially each of said media.
 4. Thecharacter recognition system of claim 2 including means synchronizingsaid source of coherent radiation pulses and said means for illuminatingsequentially each of said media with the rate at which each one of saidmedia is detected.
 5. The character recognition system of claim 1wherein said means for situating the deformed region of said coating inthe path of said radiation comprises means mechanically coupled to saidsubstrate for impelling said substrate to transport the deformed regionof said coating into the path of said radiation.
 6. The characterrecognition system of claim 5 wherein said substrate comprises a discand said means for impelling said substrate comprises a synchronousmotor.
 7. The character recognition system of claim 5 including meansfor establishing an electrical charge on the surface of said coating inthe region of said coating immediately ahead of the location at whichsaid characters are imaged onto said coating.
 8. The characterrecognition system of claim 5 wherein said source of coherent radiationpulses comprises a laser and said radiation detecting means comprises anarray of photodetectors.
 9. The character recognition system of claim 6including means for establishing an electrical charge on the surface ofsaid coating immediately ahead of the location at which said charactersare imaged onto said coating.